The gasoline engine was a marked improvement on the steam engine and it achieved its greater efficiency of twenty-eight per cent by working at a higher temperature. In the same way, the diesel engine, with an increased efficiency of up to thirty-five per cent, obtained this figure by working at even higher temperatures.
An English inventor, Herbert Akroyd-Stuart, had been working for some time on the design of an engine which could use cheap, unrefined oil as fuel. He had also suggested that by compressing the cylinder gas sufficiently it could be made to ignite of its own accord as a result of the increase in temperature caused by the quick compression.
The German engineer, Rudolf Diesel (1858-1913), working along the same lines and backed by industrialists, perfected the idea and in 1897 completed his first engine. Diesel engines do not require a carburetor. Because of their high efficiency they are now used all over the world to drive heavy trucks and buses, ships and trains, electric power plants and submarines.
The weight of the diesel engine has prevented it from being used in aircraft, where power is of greater importance than efficiency.